Numerous unreinforced vinyl siding panels are known in the prior art. The unreinforced panels are generally relatively inexpensive, and they can be embossed with attractive, simulated wood grain patterns. However, there is still a need to provide inexpensive vinyl siding panels having improved fire properties, greater tensile strength, higher flexural modulus and a lower coefficient of thermal expansion (CTE) than unreinforced prior art siding panels. The latter property is desirable in order to improve the siding panel's resistance to distortion accompanying changes in temperature. Such temperature-induced distortion is sometimes referred to as "oil canning".
Glass fibers are known in the prior art as high strength and relatively inexpensive reinforcing materials. Consequently, some workers have suggested the desirability of incorporating glass fibers into vinyl siding panels. For example, Rajewski U.S. Pat. No. 4,308,702 states that glass fibers may be used along with other conventional filler material such as additives, pigments, etc., in rigid plastic building panels produced by profile extrusion of polyvinyl chloride (PVC) and other thermoplastic polymers. Wallen U.S. Pat. No. 5,030,676 suggests a process in which an unplasticized polyvinyl chloride composition can be extrusion coated on a variety of preformed stock materials such as wood, aluminum, glass fibers and the like. Kohl U.S. Pat. No. 4,788,088 discloses a laminated plastic structure made by extruding a plastic tube around a fibrous reinforcing material. Kohl's extruder 26 has only a single orifice 30 which forms elliptical or round plastic tubing. The plastic tube is flattened around reinforcing material to form a laminate.
While the prior an contains some hints as to the desirability of incorporating glass fibers into vinyl siding panels, that result has heretofore remained unattainable at a reasonable production cost and quality of product. In addition there is still a need to provide a method and apparatus for producing glass fiber reinforced siding panels that are not wrinkled in the forming process.
It is a principal objective of the present invention to provide a vinyl building panel reinforced by a glass fiber mat and having improved fire retardance, strength, modulus and thermal expansion properties.
A related objective of the invention is to provide a commercially feasible method for making an extruded, glass fiber reinforced composite building panel.
Another objective of the invention is to provide a method and apparatus for reducing wrinkling in the composite building panel.
Additional objectives and advantages of our invention will become apparent to persons skilled in the art from the following detailed description and drawings.